Avi Savar, founding partner at the social-media agency Big Fuel, said that aside using Google+ as a focus group for hardcore customers, "I don't find too much value for a brand to spend time, energy and resources there.

Google+ users spend only three minutes on the platform every month, on average, compared to 405 minutes for Facebook users and 50 minutes for Pinterest users, according to ComScore.

Pinterest may turn out to be a big problem for Google+ in terms of attracting advertisers. Referral traffic from Pinterest to Shopify is already equal to traffic coming from Twitter, the online-store creator reports. The average order from a Pinterest user is $80, greater than that of Google or Facebook.